The exemplary embodiments relate generally to three dimensional semiconductor integration structures and, more particularly, relate to three dimensional semiconductor integration structures having through silicon via structures and offset passivation to reduce electromigration.
In semiconductor technologies, a through silicon via (TSV), also known as a through substrate via, is a conductive feature formed in a semiconductor substrate (wafer/chip). The TSV feature vertically passes through the semiconductor substrate, providing a stacked wafer/chip packaging method and allowing electrical connection between circuits in separate wafers or chips.
There are a number of ways to create a TSV. Typically, a hole is etched into the semiconductor substrate, and sometimes through an interconnect structure as well. The hole may then be lined with various isolating layers and/or various metal layers. The hole is then filled with the conductive material, typically copper (Cu), which becomes the major part of a TSV. Some TSVs are in electrical contact with the semiconductor substrate, while others are electrically isolated. Any material within the etched hole may be considered part of the TSV, so the complete TSV may include the Cu, plus a liner, and perhaps insulating layers.
The TSV may terminate on a bonding pad. A solder ball, also called a C-4 connection, may contact the bonding pad and join the bonding pad of one semiconductor chip to a bonding pad of another semiconductor chip or a package. In this manner, multiple chips may be stacked on a package to form a three dimensional silicon integration structure.
Though a conventional via shares some similarity of name with a through silicon via, it is a substantially different structure bearing little relationship. A conventional via connects wires within a die or an interconnect structure (such as a package) and may only pass through a single dielectric layer. Conventional vias are on the order of the sizes of the metal lines to which they connect, generally within a factor of three to four times the thickness in the worst case. A TSV, having to pass through an entire semiconductor substrate, may be as much as thirty times larger in diameter than the conventional via.
Electromigration can take place in any conductive material carrying a current, such as a TSV structure or a metallization layer. Electromigration is the transport of material caused by the gradual movement of electrons in a conductor. This transport of material may eventually cause a gap, or a void, in the conductive material leading to higher resistance at other connection points, or an open circuit failure when all connection is lost. To reduce the occurrence of such voids, there are rules limiting the amount of current allowed in a conductive material. Such electromigration ground rules are well known within the art.